PORTSMOUTH, Ohio, Oct. 9 -- Democratic presidential candidate Barack Obama on Thursday said rival John McCain's mortgage rescue plan "punishes" taxpayers and rewards lending institutions that created the crisis, while McCain charged that his opponent's response showed a lack of concern for homeowners.

The mortgage proposal became the latest point of strife between two campaigns that have tried to turn discussions about the economic crisis into questions about their opponent's fitness for office. Echoing a theme of the past several days, McCain said Obama's moves have shown a lack of judgment, while the senator from Illinois continued to cast his opponent's reactions as uneven and rash.

On a day when some conservatives also critiqued McCain's proposal, Obama used the "risky idea" as a way to describe McCain as a desperate candidate "lurching" from idea to idea as he tries to find an answer to the economic crisis that has roiled the presidential campaign.

"His first response to the housing crisis in March was that homeowners shouldn't get any help at all," Obama told a crowd at a minor-league baseball park in Dayton, part of a two-day swing through the battleground state of Ohio.

"Then a few weeks ago, he put out a plan that basically ignored homeowners. Now, in the course of 12 hours, he's ended up with a plan that punishes taxpayers, rewards banks and won't solve our housing crisis."

During the presidential debate Tuesday night, McCain proposed having the government buy and refinance troubled home loans. On Wednesday, his campaign said that the Treasury Department would buy the bad mortgages at face value even though home prices may have dropped below the value of the mortgages. Taxpayers would make up the shortfall.

McCain aides said that structure is necessary to make the plan work, and at town hall meeting in Wisconsin, the senator from Arizona and his running mate, Alaska Gov. Sarah Palin, slammed Obama for not supporting the proposal.

"He's opposed to us helping the homeowners of America," McCain said. "Do you want to help the homeowners of America, or do you want to help Wall Street? That's the question here."

Obama agreed on the question, just not the answer.

"Banks wouldn't take a loss, but taxpayers would take a loss," he said. "It's a plan that would guarantee that you, the American taxpayers, would lose by handing over $300 billion to underwrite the kind of greed and irresponsibility on Wall Street that got us into this mess."

Obama aides were delighted to send out copies of a critique of the plan from editors of the conservative National Review that said "McCain's plan would also be a gift to lenders who abandoned any sense of prudence during the boom years." And the Obama campaign quickly cobbled together a television ad that said McCain was "putting bad actors ahead of taxpayers. We can't afford more of the same."

Speaking at an evening rally at Shawnee State University, Obama said: "Today, millions of Americans lost more of their investments and hard-earned retirement savings as the stock market took another significant plunge. Now, it is critical that the Treasury Department move as quickly as possible to implement the rescue plan that passed Congress so we can ease this credit crisis that's preventing businesses large and small from getting the loans they need. It's causing instability in our market. Understand, this is not just an issue for big businesses or banks in New York."

On Thursday, the stock market lost nearly 700 points and dropped below 9,000 for the first time in five years. Neither McCain or Palin mentioned the stock market on the campaign trail, and their campaign did not release a comment on it.

For several weeks, McCain's campaign has become more aggressive in painting Obama as dangerous, using the word in advertisements and on the stump. The idea, aides said, is to raise fundamental questions about Obama's ability to lead the nation.

On foreign policy, they question his judgment for opposing the "surge" strategy in Iraq. On the economy, they accuse him of being a "co-conspirator" with those who caused the crisis.

At the town hall meeting, McCain charged that Obama "did not lift a finger" to stop the accumulation of bad debts by mortgage giants Fannie Mae and Freddie Mac despite what McCain said were Obama's associations with top officials of the organizations.

More than that, McCain essentially calls Obama a liar, a man whose background is one of shifting positions, inflated claims and questionable behavior. His campaign has repeatedly attacked Obama in the past week for his relationship with William Ayers, who was part of a domestic terrorist group during the Vietnam War.

In Strongsville, Ohio, on Wednesday night, Palin criticized Obama and his running mate, Sen. Joseph R. Biden Jr., as looking backward in an attempt to assign blame. When McCain took the microphone, he did just that.

He said Obama has neither told the truth about what he has done nor answered critics. Instead, McCain said, Obama has challenged his credibility. "Let me reply in the plainest terms I know," he said. "I don't need lessons about telling the truth to the American people. If I ever needed an improvement in that regard, I probably wouldn't seek the advice of a Chicago politician."

Obama has also continually couched the argument in terms of whether McCain can be counted on to be stable in a crisis. In recent days, Obama and his surrogates have emphasized words such as "lurching" and "erratic" to describe the Republican, while a campaign ad also accuses McCain of being "erratic."

"This is the kind of erratic behavior we've been seeing out of Senator McCain," Obama said in Dayton. "You remember the first day of this crisis, he came out and said the economy was fundamentally sound. Then two hours later, he said we were in a crisis.

"I don't think we can afford that kind of erratic and uncertain leadership in these uncertain times. We need steady leadership in the White House. We need a president we can trust in times of crisis. And that's why I'm running for president of the United States of America."